I agree with you that Ubuntu had a really positive impact on Linux adoption by providing a polished operating system.
That being said I think they somewhat deserve the bad opinion the Linux community has about them: Canonical decided to play solo on several critical subject instead of cooperating with others, in particular I'm thinking about upstart (a competitor for systemd) and Mir a competitor of wayland).
Their marketing is also pain point, because they brand everything as Ubuntu and don't refer to Linux at all in many of their statements (for instance, you cannot find a single occurance of the word «Linux» on their landing page[1]).